---
title: Wet Bulb Globe Temperature Meters and History
description: The wet bulb globe temperature (WBGT) is growing in popularity. More and more people are discovering WBGT meters value to OSHA requirements and heat stress.
---

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### WBGT103

![wbgt103](https://www.scientificgear.com/hs-fs/images/wbgt103small-resized-188.jpg?width=189&height=257&name=wbgt103small-resized-188.jpg)The WBGT103 is a convenient hand-held meter that provides all the thermal conditions required to measure WBGT.  Simply press the on/off button and toggle through the readings for Ambient Temperature (Ta), Relative Humidity (RH), Globe Temperature (Tg), and WBGT.  The wet bulb globe temperature index is specified by ISO-7243, which defines the following formula based on Ta (Natural Dry-bulb Temperature), Tnw (Natural Wet-blub Temperature) and Tg (Globe Temperature):

- Outdoor under sunlight: WBGT=0.7Tnw+0.2Tg+0.1Ta
- Indoor without sunlight: WBGT=0.7Tnw+0.3Tg

The dry-bulb temperature is measured by the built-in thermometer, and the wet-bulb temperature is obtained by calculating RH (relative humidity) and Ta.  The Tg is a converted value from the 24mm-diameter black hemisphere to the standard 150mm-black bulb temperature.

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# Wet Bulb Globe Temperature (WBGT) Meters and History

Thermal effects on the human body whether in a room or outdoors is significantly influenced by four environmental factors; Air Temperature, Humidity, Radiant Heat, and Wind Speed.  The WBGT (wet bulb globe temperature) consists of three factors; Humidity, Radiant Heat, and Temperature.  Reference to a WBGT index is commonly used as a guidance for environmental heat stress to prevent heat related injuries during physical exercise or work.

Specified in ISO 7243 "Estimation of heat stress on working man" is based on the WBGT index.

![wbgt setup](https://www.scientificgear.com/hs-fs/images/wbgtarmypic.jpg?width=391&height=683&name=wbgtarmypic.jpg)

 

The above sketch shows the measuring system used by the U.S. Army in order to prevent soldiers from getting heat injuries.  The height of the measuring position is 1.2 meters from the ground.  The Wet-bulb and Dry-bulb temperature is measured under natural condition with air velocity.  The Wet-bulb thermometer needs a supply of water before it is dried.  The black globe of 15cm (6 inch) diameter contains a thermometer inside.

### WBGT (web bulb globe temperature)

![IMG_0320](https://www.scientificgear.com/hs-fs/file-8160454-jpg/images/WBGT/IMG_0320.jpg?width=3466&name=IMG_0320.jpg)

 

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